FIELD OF INVENTION
The invention generally relates to an improved method and dew point measuring device for monitoring the performance of a gas drier in a turbo generator.
BACKGROUND OF THE INVENTION
The present systems use Hydrogen gas in turbo generators for taking away the heat from the heated parts inside the generator. It is cooled with the help of coolers mounted inside the turbo generator through a well-defined ventilation path. However, during the process, it may get wet due to variety of reasons. Besides coolers water leakage, the oil and water vapours may also liberate into the generator from the oil seals. To ensure dryness of the gas inside the generator, dew point temperature of H2 gas inside the generator, is monitored.
The wet Hydrogen is required to be dried with the help of a Gas drier continuously. For this purpose, a plurality of duplex gas driers are provided. H2 gas at compressor outlet is taken out to the gas drier and returned back to the generator after cooling. One gas drier is always kept in operation. The second gas drier is put in reactivation mode cyclically to regenerate the Silica Gel. While, the drier is in service, its effectiveness to dry the H2 gas may deteriorate. Hence, the dew point temperature at drier outlet is required to be monitored. The prior art systems use two number dew point temperature measuring devices to monitor the extent of moisture present respectively in hydrogen gas inside a turbo generator and at the outlet of the H2 gas drier. Two sensing devices are installed on pipelines connecting the gas drier to the generator. The difference of dew point temperatures observed at inlet/outlet of the gas drier gives direct indication of the effectiveness of the gas drier in drying of the H2 gas. A small

percentage of the gas is always drawn from the generator for drying the H2 gas which is subsequently returned to the generator. With the passage of time, the calibration characteristics of the two sensors get altered. The deterioration in the characteristics is not uniform. Hence, interpretation of the results becomes difficult.
An object of the invention is to propose a process to reliably measure over long periods the effectiveness of the performance of a gas drier towards drying of H2 gas.
Accordingly, in one aspect of the invention there is provided an improved method for monitoring the performance of at least one gas drier in a turbo generator, comprising: providing a dew point measuring device; forming a flow-circuit for the flow of H2 gas adjoining the at least one gas drier and the turbo generator, the flow-circuit being equipped with plurality of isolating valves, solenoid valves and a needle valve to control the H2 gas flow; connecting the dew-point device to the flow-circuit between the at least one gas drier and the turbo generator; providing a selector switch to operate the flow-circuit; connecting the dew-point measuring device via a cable to a distributed control system-(DCS) and/or to a conventional indicator for displaying the visual indication of the signals generated by the dew-point measuring device; putting the selector switch in a first mode causing closure of the specified solenoid valves and automatic opening of the other set of solenoid valves, the isolating valves being always kept open, the circuit causing H2 gas to flow through the valves, the dew point measuring device, outputting signals representative of dew-point temperature of H2 gas inside the turbo generator for display in the DCS; putting the selector switch in a second mode causing closure of the specified solenoid valves and opening of the other set of solenoid valves, the required flow being set by means of the needle valve, the dew-point device outputting a signal representative of dew-point temperature of H2 gas emitting from the gas drier,

The dew-point temperature of H2 gas is measured at two locations by disposing the device in a by-pass loop.
In a second aspect of the invention there is provided an improved dew-point measuring device for monitoring the performance of a gas drier in a turbo generator, the gas drier and the turbo generator being connected via a flow-circuit for the flow of H2 gas, the flow-circuit being provided with a plurality of isolating valves ,_a plurality of solenoid valves, and a needle valve, and a selector switch (5) operating the flow-circuit (4) at a first and at a second mode, the device comprising a probe connected to the flow-circuit via a flow-meter for measuring the dew-point temperature of H2 gas flowing through the flow-circuit and outputting signals representative of dew-point temperature output of the H2 gas inside the turbo generator in a first mode and the dew-point temperature output of the H2 gas emitting from the gas drier in a second mode depending upon the operation of the selector switch. The probe comprising a single moisture sensor for measuring the dew-point temperature of H2 gas at two locations in the flow-circuit, and the device is operably connected to a by pass loop.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 - Schematics Diagram of a Dew Point Temperature Monitoring System embodying the process according to the present invention.
DETAILED DESCRIPTION OF A PREFFERED EMBODIMENT
The dew point of the H2 gas at gas drier inlet (2a) and outlet (2b) of the drier (2) can be monitored reliably with the help of the dew-point measuring device. The method comprises measuring the dew points for H2 gas at two locations by connecting the dew point measuring device in a bypass loop of a flow-current

(4). The operation of the method is described herein below. With the use of the same sensor both for the sensor H2 inside the generator and at drier outlet, the effect of drift in the moisture sensor characteristics is minimized as both the measurements are equally drifted. The effectiveness of the gas drier is checked by the difference in dew point temperature at outlet and inlet points. One gets exact idea of the effectiveness of the gas drier to decide switching over of the drier to the alternative one to continue the operation of Hydrogen drying. Once, the dew points at inlet (2a) and outlet (2b) tend to eqalise, that indicates that Silica Gel or the other drying agent put inside the gas drier requires regeneration. Hence, alternate gas drier is switched ON and this drier is taken out of service.
The isolating valves V-l and V-2 are always kept open for operation of the system. To monitor dew point of the Hydrogen gas inside generator (1), the selector switch (5) is put in Mode-1. It causes closure of solenoid valves SV-3 and SV-4 and opening of solenoid valves SV-1 and SV-2 automatically. The circuit causes hydrogen gas to flow through V-2, SV-1, coalescing filter (6), flow meter (7), probe (3), SV-2, V-l and back to the generator (1). The required flow may be adjusted with the help of flow meter (7). The dew point meter gives dew point temp output as 4-20mA signal for control room. This is used for visual indication in Distributed Control System (DCS) or in conventional indicators.
To monitor dew point temperature of H2 gas emitting from the gas drier to check effectiveness of the drier, Mode-2 is selected. It causes closure of solenoid valves SV-1 and SV-2 and opening of solenoid valves SV-3 and SV-4. The required flow is set during initial commissioning with the help of needle valve NV-1. The dew point meter gives dew point temp output as 4-20mA signal for control room. This is used for visual indication I Distributed Control System (DCS) or in conventional indicators.

OPERATING MODES
MODE- 1 :- TO KNOW DEW POINT OF H2 IN GENERATOR. THIS IS THE NORMAL MODE OF OPERATION.
VALVE TO BE OPENED:- SV-1, SV-2.
VALVE TO BE CLOSED:- SV-3, SV-4. MODE - 2 :- TO KNOW EFFECTIVENESS OF GAS DRIER
VALVE TO BE OPENED:- SV-3, SV-4
VALVE TO BE CLOSED:-SV-l, SV-2 NOTES :-
1- GAS FLOW TO BE SET WITH TEH HELP OF VALVE ON FOW METER IN MODE - 1.
2- NV-1 TO BE SET FOR REQUIRED FLOW IN MODE-2 AND TO BE LEFT AS IT IS.
3- VALVE NV-1 SHOULD PREFERABLY BE GLANDLESS, BUTYL RUBBER, DIAPHRAM TYPE WITH THREADED ENDS, LEAK PROOF FOR H2 SERVICE.
4- SOLENOID VALVE SV-1 TO SV-4 SHALL BE EXPLOSION AND LEAK PROOF WITH OPERATING VOLTAGE 24VDC / 240V AC.
5- VALVES V-1 & V-2 TO BE ALWAYS KEPT OPEN.

WE CLAIM
1. An improved method for monitoring the performance of at least one gas drier (2) in a turbo generator (1), comprising:
Providing a dew point measuring device (3);
Forming a flow-circuit (4) for the flow of H2 gas adjoining the atleast one gas drier (2) and the turbo generator (1), the flow-circuit (4) being equipped with plurality of isolating valves (V1,V2), solenoid valves (SV1-SV4) and a needle valve (NV-1) to control the H2 gas flow;
Connecting the dew-point device (3) to the flow-circuit (4) between the at least one gas drier (2) and the turbo generator (1);
Providing a selector switch (5) to operate the flow-circuit
(4);
- Connecting the dew-point measuring device (3) via a cable
(8) to a distributed control system-(DCS) and/or to a
conventional indicator for displaying the visual indication of
the signals generated by the dew-point measuring device
(3);
- Putting the selector switch (5) in a first mode causing
closure of the solenoid valves (SV-3, SV-4) and automatic
opening of the solenoid valves (SV-1, SV-2), the isolating
valves (V-1, V-2) being always kept open, the circuit
causing H2 gas to flow through the valves (V2,SV1,SV2,
SVi), the dew point measuring device (3) outputting
signals representative of dew-point temperature of H2 gas
inside the turbo generator for display in the DCS;
- Putting the selector switch (5) in a second mode causing
closure of the solenoid valves (SV-1, SV-2) and opening of
The solenoid valves (SV-1, SV-2), the required flow being set by means of the needle valve (NV-1), the dew-point device outputting a signal representative of dew-point temperature of H2 gas emitting from the gas drier, characterized in that the dew-point temperature of H2 gas is measured at two locations by disposing the device (3) in a by-pass loop (4). 2. An improved dew-point measuring device for monitoring the performance of a gas drier (2) in a turbo generator (1), the gas drier (2) and the turbo generator (1) being connected via a flow-circuit (4) for the flow of H2 gas, the flow-circuit (4) being provided with a plurality of isolating valves (V1, V2) a plurality of solenoid valves (SV1, SV2, SV3, SV4) and a needle valve (NV1), at a first and at a second mode, and a selector switch (5) operating the flow-circuit (4), the device comprising;
- A probe (3) connected to the flow-circuit (4) via a flowmeter (7) for measuring a dew-point temperature of H2 gas flowing through the flow-circuit (4) and outputting signals representative of dew-point temperature output of the H2 gas inside the turbo generator (1) in a first mode, and a dew-point temperature output of the H2 gas emitting from the gas drier (2) in a second mode depending upon the operation of the selector switch (5), characterized in that the probe (3) comprising a single moisture sensor for measuring the dew-point temperature of H2 gas at two locations in the flow-circuit (4), and in that the device is operably connected to a by pass loop. 3. The device as claimed in claim 2, wherein a coalescing filter (6) is disposed in the flow-circuit (4) flowing H2 gas through the by-pass loop to the flow-meter (7).
4. An improved method and dew point measuring device for monitoring the performance of a gas drier in a turbo generator substantially as herein described and illustrated in the accompanying drawing.